1. Field of the Invention
The present invention relates to a V-belt type transmission, and more particularly to a V-belt type transmission for a vehicle wherein power is transmitted using a V-belt mounted spanning between pulleys.
2. Description of the Background Art
In a V-belt type transmission of the background art, wherein a V-belt is mounted spanning between a pair of pulleys. The pair of pulleys includes a fixed pulley half and a movable pulley half. Power is transmitted in a continuously various speed change mode. The fixed pulley half is fixed to an end portion of a crankshaft and the movable pulley half is disposed inside the fixed pulley half. According to arrangements in the background art, the fixed pulley half is clamped and fixed with a nut that is threadingly engaged with a male screw formed on an end portion of the crankshaft.
FIG. 6 shows an example of the foregoing type of arrangement as described in JP-A No. Hei 9-264391 of the background art. A V-belt type transmission used in a scooter type motor vehicle is described. FIG. 6 shows a pulley 02 mounted on a crankshaft 01 side of the V-belt type transmission.
A male screw 01a and a serrated portion are formed so as to project on an end portion of the crankshaft 01. A fixed pulley half 03, which is serration-fitted on the end portion of the crankshaft, is clamped and fixed with a nut 05 which is threadingly engaged with the male screw 01a. An axially slidable, movable pulley half 04 is supported inside the fixed pulley half 03.
A V-belt 06 is arranged between the fixed pulley half 03 and the movable pulley half 04, and a centrifugal weight 07 is provided on the back of the movable pulley half 04. The centrifugal weight 07, which operates in accordance with the speed of rotation of the crankshaft 01, moves the movable pulley half 04 axially to change the winding diameter of the V-belt. Accordingly, power is transferred in a continuously various speed change mode to the rear wheel side.
Cooling fins 03a are formed on the back of the fixed pulley half 03. By rotation of the cooling fins 03a, air is introduced through an air inlet pipe 09 provided in a belt cover 08 to cool a power transfer mechanism and thereby improve durability.
When outside air is introduced into the inside of the power transfer cover 08, a filter or the like is sometimes provided in the outside air introducing portion to remove dust or other foreign matters. However, fine dust or the like and water get into the inside of the belt cover 08 and reach the threadingly engaged portion of the male screw 01a and the nut 05 at the end portion of the crankshaft 01. This may result in rusting and the threadingly engaged portion and the nut 05 becoming seized in place.
Moreover, a posture varying force of the fixed pulley half 03 against the crankshaft 01, which is induced by a belt reaction force, acts detrimentally upon the nut 05. This force acting on the nut 05 which is clamped on the outside of the fixed pulley half 03 in threaded engagement with the end portion of the crankshaft has been problematic in systems of the background art. Consequently, in order to ensure a sufficient strength, the threadingly engaged portion of the male screw 01a and the nut 05 is often made larger in size, which may result in an obstruction to the introduction of the outside air.
In the case where the crankshaft 01 is formed integrally with crank pins by molding, center holes for supporting the crankshaft 01 at both shaft ends must be formed respectively with male screws 01a at the shaft ends at the time of machining the crankshaft. As shown in FIG. 6, the center hole 01b formed in each male screw 01a is restricted to a size smaller than the size of the male screw 01a. Thus, a sufficient support area is not obtained and it is difficult to attain a high machining accuracy. Accordingly, machinability is poor and expensive.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
It is an object of the present invention to provide a V-belt type transmission capable of clamping a fixed pulley half securely to a crankshaft.
It is a further object of the present invention to prevent the entry of dust and water into a pulley that has been engaged with a threaded connection to an end portion of a crankshaft, to prevent rusting, etc. of the threaded connection.
These and other aspects of the present invention are accomplished by a V-belt transmission comprising a crankshaft having a drive end; a V-belt arranged between a fixed pulley half fixed to an end portion of the crankshaft and an axially movable pulley half supported on the crankshaft in a position laterally opposite to the fixed pulley half; and a bolt securing the fixed pulley half to the end portion of the crankshaft, the bolt threadingly engaged with a female screw portion formed within an interior portion of the end portion of the crankshaft.
These and other aspects of the present invention are further accomplished by a V-belt transmission comprising a crankshaft having a drive end; a driving pulley operatively connected to the crankshaft; and a driven pulley operatively connected to a rear wheel drive section of the transmission; a V-belt arranged between the driving pulley and the driven pulley, wherein the driving pulley includes a fixed pulley half fixed to an end portion of the crankshaft and an axially movable pulley half supported on the crankshaft in a position laterally opposite to the fixed pulley half; and a bolt securing the fixed pulley half to the end portion of the crankshaft, the bolt threadingly engaged with a bolt hole formed within an interior portion of the end portion of the crankshaft.
Since the fixed pulley half is clamped with a bolt which is threadedly engaged with a female screw formed in the interior of an end portion of the crankshaft, the threadedly engaged portion of the bolt lies within the interior of the end of the crankshaft. Accordingly, the entry of dust and water can be prevented and the transmission can be protected against rust, corrosion, etc.
Further, this arrangement prevents the formation of rust and limits the possibility of seizing of the bolt with the bolt hole. The threaded portion of the bolt can also be made longer and stronger without interfering with the lateral dimensions of the crankshaft or transmission case.
When outside air is introduced from the outside air inlet port and a power transfer mechanism is cooled with the cooling fins, even if the bolt fitted in the end portion of the crankshaft is exposed to dust or water, it is possible to protect the threadedly engaged portion that is secured within the interior of the crankshaft.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.